Tolerable Crack Widths

Hotline Question

We placed concrete for an elevated deck that will be covered with carpet. There are some cracks that the owner wants us to fill with epoxy. For elevated concrete slabs on metal decking, is there a standard document that requires epoxy injection if cracks open wider than a given amount?

Hotline Answer

We don't know of any document that requires epoxy injection for cracks exceeding a specified width. Because a concrete deck is so highly restrained by the metal decking and steel-stub shear connectors, consultant J. Thomas Ryan says cracks are inevitable in concrete decks supported by a structural-steel frame (See "Let It Crack," Concrete Construction, August 1999, pp. 37-39). Ryan advises that any cracks wide enough to affect the service ability of the floor can be patched. This suggests that usually such cracking isn't a structural-strength issue, so structural repair such as epoxy injection shouldn't be needed.

Check with the designer to ensure that the crack doesn't indicate a structural problem. If no structural problem is indicated, but the crack is wide enough to distort the carpeting, it should probably be routed and patched with a cementitious repair material. Appearance isn't a consideration since the carpeting will cover any cracks and patches. It won't be visible.

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